1. Technical Field
Embodiments of the present invention relate to a capacitive load driving device for applying a drive signal to a capacitive load, such as a piezoelectric element, to thereby drive the capacitive load. Embodiments of the invention further relate to a fluid ejection device that includes an actuator as the capacitive load and that applies the drive signal to the actuator to thereby eject a fluid.
2. Related Art
In the case of power-amplifying the drive waveform signal composed of a predetermined voltage waveform with a digital power amplifier to form a drive signal that is applied to an actuator formed of a capacitive load, a modulator performs a pulse modulation on the drive waveform signal to form a modulated signal, the digital power amplifier performs a power amplification on the modulated signal to form an amplified digital signal, and a low pass filter smoothes the amplified digital signal to form the drive signal.
If the waveform of the drive signal is important, there are some cases in which a feedback signal is formed by setting forward or advancing the phase of the drive signal. The difference value between the feedback signal and the drive waveform signal obtained by the subtraction section is used as an input signal to the modulator. According to JP-A-2005-329710 (Document 1), it is arranged that the output of the low pass filter composed of a quadratic low-pass filter, namely the drive signal, is fed back as a first feedback signal, and at the same time, the output of the digital power amplifier, namely the amplified digital signal is made to pass through a first-order low-pass filter and is then fed back as a second feedback signal. Since the first-order low pass filter leads the quadratic low pass filter in phase, it is intended to compensate the waveform of the drive signal with the phase-leading component. It should be noted that the frequency of the pulse modulation by the modulator is called a modulation frequency or a carrier frequency.
However, since the signal, which is fed back with its phase set forward in Document 1, is not the drive signal applied to the actuator, but is the amplified digital signal as the output of the digital power amplifier, the waveform of the drive signal cannot sufficiently be compensated.